Machines of this type have existed for a long time. Thus, U.S. Pat. No. 3,603,216, filed in 1968, describes a machine in which a multi-ply paper-like material is guided firstly in a converging chute which is a truncated pyramid in shape and which becomes thinner downstream so that the longitudinal edges of the material are folded perpendicularly to the axis, and then secondly in a gear assembly between which the material travels. The central band of the resulting strip is grabbed by the teeth of the gears and pulled downstream as it is nipped by these gears. The material is simultaneously compressed or coined, and the various layers are pressed together forming the coined strip. The product made by the machine comprises consequently a central coined strip and two pillow-like edges, and is suitable for padding shipping cases or boxes.
The main characteristic of this type of machine is that the same gears simultaneously pull the paper-like material downstream, and crumple and coin the multi-ply strip to connect the inwardly rolled edges to the central strip.
In practice, this plurality of functions can cause problems, these have been solved by various solutions, none of which is entirely satisfactory. Thus, when the pressure exerted on the sheets is sufficient to pull them downstream, the said sheets sometimes get torn up. On the other hand, if the pressure is reduced, the central strip is not held together firmly enough and sometimes the pillow-like edges come open, thus the material can consequently not be used as a cushioning dunnage product.
One of the proposed solutions to reconcile the two above requirements is described in patent No. EP-A-0 427 834 and is a gear-like stitching assembly having gear like members disposed in a meshed condition, characterized in that the teeth of at least one of the gear-like members have projections thereon for perforating the multi-ply formed material along the central coined section of the produced pad like cushioning dunnage product.
However, the central coined area becomes more fragile, particularly where the projections of the teeth have made perforations, which are in fact beginnings of tears. The described machine can then only be used with superimposed sheets of high quality kraft paper, which is also much more expensive.